1. Field of the Invention
This invention relates generally to inorganic binders, specifically to such inorganic binders which employ glass, preferably waste glass.
2. Description of the Related Art
Waste glass poses serious problems for municipalities worldwide, since glass is not biodegradable and only a small fraction of these waste glass can be reused by the primary market namely, the bottling and container industry.
Use of waste glass in a coarsely divided form, or as aggregate, in concrete has been attempted in the past. The main challenge, however, is to avoid a detrimental chemical reaction between the cement and glass aggregate, termed Alkali-Silica Reaction (hereinafter "ASR"), which causes cracking and degradation of concrete containing glass aggregate. For example, U.S. Pat. No. 5,810,921 to Baxter et al. ("the Baxter '921 patent") provides a glass formula comprising chromium for incorporation in glass-concrete compositions that does not undergo ASR. Still, U.S. Pat. No. 5,803,960 to Baxter ("the Baxter '960 patent") further provides a glass formulation with lithium in its glass-concrete composition to avoid ASR.
Attempts have also been made to use waste glass in a finely divided form, or as powder, in concrete. Waste glass powder has been shown to exhibit some degree of pozzolanic property and be able to partially replace Portland cement in concrete. For example, J. F. Archibald et al., "Ground Waste Glass as a Pozzolanic Consolidation Agent for Mine Backfill", CIM Bulletin, Vol. 88, pp.80-87, 1995, provides that up to 20% of Portland cement can be substituted by ground waste glass without substantial loss of strength in the final product. However, the pozzolanic reactivity of waste glass powder has proven to be extremely low. It does not readily react with lime, nor does it bear any binding ability in itself. Therefore, a need exists to impart self-binding property to glass, preferably waste glass.
Waste glass includes post-consumer glass articles such as beverage bottles, window glass, and any and all other glass containers. The general chemical composition of a glass has a general formula of Na..sub.2 O--CaO--SiO.sub.2, commonly known as soda-lime glass. Specifically, glass comprises, in weight percentage, about 13.6% to 14.4% Na.sub.2 O, 10.7% to 12.2% CaO, and 71.3% to 73.5% SiO.sub.2. A glass containing this chemical formula tends not to exhibit any cementitious or hydraulic property. To make a glass cementitious, i.e., self-binding upon adding water as hydraulic cement does, its chemical composition has to be specially formulated. For example, U.S. Pat. No. 3,498,802 to Bickford et al ("Bickford") provides a glass cement which comprises, in weight percentage of about 80% to 94% SiO.sub.2 and 6% to 20% Na.sub.2 O and/or K.sub.2 O which hardens at a temperature of 100.sup.0 -200.degree. C. U.S. Pat. No. 3,720,527 to Farrauto et al ("the Farrauto '527 patent") provides a hydraulic glass cement comprising, in weight percentage, about 15% to 85% Na.sub.2 O and/or K.sub.2 O, 10% to 80% SiO.sub.2, and 3% to 20% P.sub.2 O.sub.5. U.S. Pat. No. 3,743,525 to Farrauto et al ("the Farrauto '525 patent") provides a hydraulic glass cement which comprises, in weight percentage, about 20% to 80% SiO.sub.2, 5% to 40% Na.sub.2 O and/or K.sub.2 O, 5% to 70% RO, wherein RO consists of 0% to 30% MgO, 0% to 50% CaO, 0% to 70% SrO, and 0% to 35% BaO, and 5% to 15% NaH.sub.2 PO.sub.4 and/or KH.sub.2 PO.sub.4. U.S. Pat. No. 4,440,576 to Flannery et al ("Flannery") provides a hydraulic glass cement comprising, in terms of mole percentage on the oxide basis, about 60% to 76% SiO.sub.2, 15% to 30% K.sub.2 O, and 2% to 15% total of at least one metal oxide selected from the group of 0% to 10% Al.sub.2 O.sub.3, 0% to 5% TiO.sub.2, 0% to 5% MoO.sub.3 and 0% to 5% WO.sub.3. The glass powder may also contain a phosphate component. Unfortunately, waste glass has chemical composition dissimilar to those of prior art hydraulic glass cements and thus does not harden readily with water. Since the chemical composition of glass is set, it would require re-melting of the glass and adding other minerals in the melt if the prior art compositions were to be achieved. Of course, this high-temperature glass melting process is energy-intensive and expensive. Hence, it is highly desirable for glass having a self-binding property yet not requiring a re-melting process to change its chemical composition.
Conventional pozzolanic materials or pozzolans include natural pozzolans such as volcanic tuffs and calcined clays and some industrial by-products such as fly ash and granulated blast furnace slag. These materials exhibit various degrees of pozzolanic reactivity. Some of them such as granulated furnace slag and Class C fly ash are highly pozzolanic and posses some cementitious property. Their wide use as a partial replacement for cement represents its versatile applicability. Attempts were made to increase the cementitious property of pozzolanic materials. Activation is a commonly known method. Activation is achieved either chemically by adding to the base pozzolanic material various alkali activators, or thermally by curing base pozzolanic material and activator mixture at elevated temperatures. For example, U.S. Pat. No. 4,997,484 to Gravitt et al ("Gravitt") provides a cement comprising Class C fly ash, 0.4% to 4.2% of an alkali metal activator, preferably potassium hydroxide, and 0.6% to 5% citric acid. U.S. Pat. No. 5,565,028 to Roy et al ("Roy") relates to cement comprising Class C fly ash and solutions of hydroxides of lithium, sodium, and potassium having a pH of about 14.69 or higher. U.S. Pat. No. 5,601,643 to Silverstrim et al ("Silverstrim") relates to a cementitious binder mixture comprising Class F fly ash and an alkali metal or alkaline earth metal silicate, which rapidly yields high strength when cured under elevated temperature. Unfortunately, non of these references teaches or suggests whether the method of activation is applicable to glass in general, nor does it teach how to activate glass. Glass differs from fly ash and granulated blast furnace slag like pozzolanic materials chemically, and has a different mineralogical composition and physical structure, thus, an effective method remains to be sought for glass having self-binding property and for rapid setting and high strength waste glass binders.
Other examples relating to methods of making glass products are further described below:
U.S. Pat. No.: 3,963,503 issued to Mackenzie ("Mackenzie") relates to an improved method of making glass products comprising mixing particulate used-container glass with a selected treating agent to form a unique glass mix. The used-container glass has a pre-selected approximate concentration range of foreign inclusions and an average reflectance of about 5% to about 95%. The mixture is heated to a temperature and pressure above the sintering and softening point of the glass, but below its melting point and within a range sufficient to activate the treating agent to either foam or fill the glass. In the latter case, increased pressure is applied to form the glass into a hard-pressed product, such as a tile appearance. In the former case, foamed glass of distinctive appearance is produced. The used-container glass includes a plurality of particles of various colors and the pressed product may have oxide pigments embedded in the surfaces thereof. The treating agent can be dolomite or other suitable treating agent.
U.S. Pat. No.: 4,116,703 issued to Stempin et al. ("Stempin") disclose composite foamable cement. Stempin relates to an inorganic cement mixture capable of being thermally foamed in situ, consists essentially by weight of 8-20% of crystalline hydraulic cement, 22-35% of a hydraulic cement in the form of a glass powder, and 45-70% quaternary ammonium silicate solution. The mixture can be set as a cement and thermally foamed to unite two bodies and serve as a spacer and a support to maintain them in spaced relation.
U.S. Pat. No.: 5,720,835 issued to Lingart et al. ("Lingart '835 Patent") relates to a decorative construction material and methods of its production. A decorative construction material such as a glass tile is produced from recycled glass granulate, and exhibits a smooth, external surface substantially free from defects on one side of the tile. One or two layer tiles may also be produced according to Lingart's '835 patent. A binder, together with a control of the maximum temperature and temperature gradient in the layers, if applicable, is used during manufacture to ensure a substantially flawless outer surface.
U.S. Pat. No.: 5,803,960 issued to Baxter ("Baxter '960 Patent") relates to a glass formula for avoiding ASR. Baxter relates generally to a glass formula for incorporating glass/concrete compositions. The glass contains lithium. Alkali-Silica Reaction is avoided in the glass/concrete compositions.
U.S. Pat. No.: 5,810,921 issued to Baxter ("Baxter '921 Patent"). Baxter uses a waste glass in concrete. The present invention relates generally to a glass formula for incorporation of glass-concrete compositions. The glass contains chromium. A detrimental reaction between the cement and the chromium glass and/or a reactive aggregate glass is suppressed in the set glass-concrete compositions.
U.S. Pat. No.: 5,900,202 issued to Lingart et al. ("Lingart '202 Patent") relates to a method of making glass silicate tiles. The method according to Lingart '202 patent includes making glass-silicate tiles by pouring an input raw material containing glass granulate into a heat-proof mold, wetting the input raw material and making an initial blank thereby, heat treating of the blank by gradual heating and by gradual cooling by stages with holding period between the stages wherein a first heating stage is performed predominantly by heating a bottom side of the blank with higher speed of heating of a lowering layer than of an upper layer of the blank to accelerate gases to release the blank through the upper layer up to reach of the temperature of beginning of glass granulate sintering (T.sub.f) in the lower layer, and the temperature not exceeding a glass granulate transformation temperature (T.sub.g) in the upper layer, a first holding period at these condition to expel generated gases, and heating the upper layer.
In view of the foregoing, there is a long felt need to device a composition and a method for glass that has a self-binding property which does not require a high temperature and high energy re-melting process and is capable of achieving high strength in a substantially shorter time than is known in the art.